ccl/sqlproxyccl: complete connection migration support in the forwarder

Informs #76000. Builds on top of #77109 and #77111.

This commit completes the connection migration feature in the the forwarder
within sqlproxy. The idea is as described in the RFC.

A couple of new sqlproxy metrics have been added as well:
- proxy.conn_migration.requested
- proxy.conn_migration.accepted
- proxy.conn_migration.rejected
- proxy.conn_migration.success
- proxy.conn_migration.error
- proxy.conn_migration.fail
- proxy.conn_migration.timeout_closed
- proxy.conn_migration.timeout_recoverable

For more details, see metrics.go in the sqlproxyccl package.

Release note: None

pkg/ccl/sqlproxyccl/BUILD.bazel

@@ -41,6 +41,7 @@ go_library(
         "//pkg/util/stop",
         "//pkg/util/syncutil",
         "//pkg/util/timeutil",
+        "//pkg/util/uuid",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_cockroachdb_logtags//:logtags",
         "@com_github_jackc_pgproto3_v2//:pgproto3",
@@ -81,6 +82,7 @@ go_test(
         "//pkg/sql/pgwire",
         "//pkg/sql/pgwire/pgerror",
         "//pkg/sql/pgwire/pgwirebase",
+        "//pkg/sql/tests",
         "//pkg/testutils",
         "//pkg/testutils/serverutils",
         "//pkg/testutils/skip",
@@ -93,6 +95,7 @@ go_test(
         "//pkg/util/stop",
         "//pkg/util/syncutil",
         "//pkg/util/timeutil",
+        "@com_github_cockroachdb_cockroach_go_v2//crdb",
         "@com_github_cockroachdb_errors//:errors",
         "@com_github_jackc_pgconn//:pgconn",
         "@com_github_jackc_pgproto3_v2//:pgproto3",